In many fuel supply systems applicable to internal combustion engines, fuel injectors are used to inject fuel pulses into the engine combustion chamber. A commonly used injector is a closed-nozzle injector which includes a nozzle assembly having a spring-biased nozzle valve element positioned adjacent the nozzle orifice for allowing fuel to be injected into the cylinder. The nozzle valve element also functions to provide a deliberate, abrupt end to fuel injection, thereby preventing a secondary injection which causes unburned hydrocarbons in the exhaust. The nozzle valve is positioned in a nozzle cavity and biased by a nozzle spring so that when an actuated force exceeds the biasing force of the nozzle spring, the nozzle valve element moves to allow fuel to pass through the nozzle orifices, thus marking the beginning of the injection event.
Internal combustion engine designers have increasingly come to realize that substantially improved fuel supply systems are required in order to meet the ever increasing governmental and regulatory requirements of emissions abatement and increased fuel economy. As such, one aspect of fuel supply systems that has been the focus of designers is the use of piezoelectric actuators in fuel injectors.
In general, piezoelectric actuators have long been recognized as highly desirable for use in systems requiring extremely fast mechanical operation in response to an electrical control signal. For this reason, piezoelectric actuators have received considerable attention by designers of fuel supply systems for internal combustion engines. Such designers are continually searching for ways to obtain faster, more precise, reliable, and predictable control over the timing and quantity of successive fuel injections into the combustion chambers of internal combustion engines to help meet the economically and governmentally mandated demands for increasing fuel economy and reduced air pollution. If such goals are to be attained, fuel control valves must be designed to provide extremely fast and reliable response times.